Hi guys,
I'm on this part of the video and when I press E and the S I can only extrude outwards. When I try to extrude inwards (inset) nothing seems to happen.
Glad to see you solved the problem.
Double faces or verts, is very common for new learners of Blender.
Having said that, it's still fairly common amongst more seasoned users.
It is just knowing when and where they can arise, and removing them before it becomes a problem.